Transcript Supernovae Type II

1. After fusion processes fizzle out,
there is some gravitational collapse
which causes heating to T ~1010 K. This
is sufficient to trigger two
processes:
(i) Photo-disintegration of iron and the
subsequent photo-disintegration
of the products, eventually leading to
complete “inverse fusion,”
with products p and n:
γ + 56Fe → 13 4He + 4n ; γ + 4He → 2p
+ 2n
(ii) Inverse beta decay. When electrons
have K > 3.7 MeV then the
following can occur:
e- + 56Fe → 56Mn + νe
and by time we get down to nucleons:
e- + p → n +νe
Note that the Fermi energy of the
degenerate electron gas is ~4
MeV at a density of 1012 kg/m3, so there
are plenty of electrons which can trigger
these inverse beta decays.
2. The processes above are endothermic, that is
they remove kinetic energy (and hence fluid
pressure) from the core. The unstable core now
quickly collapses.
3. The iron core is now in free fall. The time of
fall to a much smaller equilibrium radius is
100 ms.
4. During collapse, the neutronization processes
proceed rapidly. Neutrinos result as well, and
these mostly exit the star. This
neutrino emission represents about 1% to 10%
of the total emission,
the remainder resulting from subsequent steps.
5. The collapse ends when the core reaches
nuclear density. Actually, the
density exceeds nuclear briefly by what is
estimated to be a factor of 2
to 3.
6. The core now strongly bounces back to
nuclear density from the supernuclear
density. We can think of the protons and
neutrons as bags of
quarks bound together by very strong springs
(spring constant 10
GeV/fm2) which are compressed by the
collapse, but then spring back
to equilibrium, thus the bounce.
7. The bounce sends a shock wave outward at
high velocity, blowing out
the remaining stellar atmosphere in the process.
Once the shock reaches
the outer atmosphere, the photons emitted by
recombination, powered
by the shock itself and by subsequent nuclear
decays, become the visible
supernova explosion.
8. The core will radiate away its huge energy
content in neutrinos and the remnant core will
settle down into a neutron
star. The radius is something like 15 km,
depending on initial core
mass, but has a mass of 1.4 to about 3 M.
9. The neutron-rich shock, meanwhile, will
induce creation of elements
heavier than iron by neutron capture.
10. The shock continues into interstellar space
at speeds of c/10. For
example, the crab neubula, resulting from the
1054 A.D. supernova is
large and still expanding.
11. The neutron star may become visible in
radio as a pulsar, depending on
rotation and magnetic fields. The crab’s neutron
star is indeed a very
“loud” pulsar, faithfully producing a radio burst
once per revolution,
every 33.3 ms.